1. Field of the Invention
The present invention relates to electrodes for resistance or elective spot welding, and particularly to construction of such electrodes.
2. Prior Art
In resistance spot welding, it is often difficult to prevent cross contamination of the material of the welding electrode onto the workpiece being welded. In those situations when the welded workpiece is subjected to further processing step, such as plating, cross contamination is undesirable. Often the contamination makes it difficult to plate over the workpiece. An example of this is when a nickel terminal pin is spot welded to the casing of an electrical energy power source for an implantable medical device. Copper is typically used for the welding electrode. However, copper contamination of the nickel surface makes it extremely difficult, if not impossible, to gold plate over the pin. In an implantable power source, the nickel pin welded to the battery or capacitor casing serves as one of the casing terminals. A second terminal pin electrically insulated from the casing by a glass-to-metal seal is the opposite polarity terminal.
What is needed, therefore, is a welding procedure for connecting a workpiece material to a substrate, such as a terminal pin to a casing for an electrical energy power source, that does not result in cross-contamination of the welding electrode material onto the workpiece material.
The present invention describes a resistance welding electrode that is particularly suited for spot welding a workpiece to a substrate without cross-contaminating specific portions of the workpiece. This is done by sheathing an internal surface of the welding electrode with a thermoplastic polymeric material. Then, there is only contact between the welding electrode and the workpiece at the very distal end of the electrode adjacent to where the workpiece is to be connected to the substrate. Contamination in this area is not detrimental because subsequent workpiece plating does not take place there.
These and other aspects of the present invention will become increasingly more apparent to those skilled in the art by reference to the following description and the appended drawings.